The machine crunch is a machine-based exercise targeting the abdominal muscles. It involves sitting upright in the machine and curling the torso down against a pre-set level of resistance. On some machines, the knees also curl up toward the torso. Crunch machines usually use extra resistance in the form of selectorized weight stacks or plate loading, and are often performed for moderate to high reps, such as 8-12 reps per set or more, as part of the ab-focused portion of a workout.
